(a) Field of the Invention
The present invention relates to a communication method in a peer aware communication system and an apparatus for transmitting/receiving by using the same.
(b) Description of the Related Art
There is no entity for managing all communication links in direct communication between terminals, unlike the existing infra network. Accordingly, each terminal has to individually search neighboring terminals and to fairly allocate radio resources to them through message sharing between the neighboring terminals. When direct communication is performed in an allowable band, a terminal is synchronized to a base station and may share allocation information with the base station in a process of allocating radio resources, and thereby it is possible to minimize interference or signal collision between terminals although a large number of terminals are involved in direct communication.
However, when direct communication is performed in an unlicensed band, radio resources are shared with terminals in a state in which only loose synchronization between the terminals is matched. The radio resource sharing may be performed with a carrier sensing multiple access (CSMA) in a wireless local area network (WLAN) generally used in an unlicensed band. When a CSMA-based wireless access scheme is used for direct communication in an unlicensed band, if the number of terminals involved in the direct communication increases, the overall transmission performance is degraded.
To solve such a problem, a scheme for using a synchronous frame structure for direct communication in an unlicensed band has been researched, and recently, standardization for the scheme has been underway. When using the synchronous frame structure, if there are a large number of terminals that simultaneously access by using direct communication, it is possible to minimize signal collision between terminals by previously scheduling transmission time for each terminal. Accordingly, the synchronous frame structure has higher transmission efficiency than that of an asynchronous-based CSMA scheme if the number of terminals simultaneously accessing increases in a direct communication-based peer aware communication system. To use the synchronous frame structure, however, time synchronization between terminals involved in direct communication has to be matched.
An orthogonal frequency division multiplexing (OFDM) transmission scheme is used in a peer aware communication system. In this case, in order to use the synchronous frame structure, the initialization for frame transmission time and OFDM symbol transmission time is needed in a transmission initialization process. Also, a receiving end has to estimate and compensate a carrier frequency error of a transmitting end and the receiving end to minimize interference between subcarriers in the receiving end.
In addition, when a synchronous demodulation scheme is used in a receiving end, channel estimation is needed. Generally, in the OFDM transmission scheme, the transmitting end and the receiving end transmit a previously promised signal pattern in a form of preamble for synchronization of the symbol transmission, frequency synchronization, and channel estimation. The preamble used in a peer aware communication system has to be separated from the preamble used in a system that is used in an unlicensed band such as a WLAN.
Unlike the allowable band for a specific communication system, a plurality of communication devices using different transmission schemes coexist with each other in the unlicensed band, while they may serve as interference each other. For example, a terminal for WLAN and a terminal for peer aware communication are used in the same environment, while they cause interference with each other. To reduce the interference, the channel occupation is recognized so that collisions with systems using different communication standards are minimized. For this, when there are an existing WLAN system and a peer aware communication system, the existing WLAN system needs a method for determining whether a channel is occupied by the peer aware communication system. At this time, the standards of the hardware and software are not changed in the existing WLAN system, and thereby it is preferred to add corresponding functions to the peer aware communication system which is being developed.
Since the peer aware communication system uses time division multiple access in accessing channel resources, signals are discontinuously transmitted even though data transmission starts after interference sensing. Therefore, even though a terminal of the peer aware communication occupies a channel and is then performing data transmission, a case in which other systems such as a WLAN system are unaware of the channel occupation by the terminal of the peer aware communication can occur. In this case, the peer aware communication system and the WLAN system simultaneously transmit signals, and thereby transmission performance is sharply degraded by signal collision between them.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.